The specific aims of this proposal are to identify additional mitochondrial disease patients, characterize their phenotypes, define the oxphos and ROS defects in skeletal muscle, and perform molecular genetic analysis to define the molecular basis of the defects. No research subjects have yet been admitted to the GCRC. However, the Molecular Cell Biology Laboratory was used to transform and store immortal Epstein-Barr virus lymphoblast cell lines from patient samples sent directly to the lab. The cell lines will serve as a permanent DNA/RNA resource, as well as an in vitro model system for molecular genetics investigations.